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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: question about nullptr
Date: Sun, 07 Jul 2024 00:04:40 -0700
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Lawrence D'Oliveiro <ldo@nz.invalid> writes:
> On Sat, 6 Jul 2024 14:51:19 +0100, bart wrote:
>> Using actual zero for a pointer value is crass. This wouldn't work for
>> example:
>> 
>>     char *p = 3;
>
> But of course this does:
>
>     char *p = 0;
>
> From the C23 spec, I found this footnote in §6.6:
>
>     A named constant or compound literal constant of integer type and
>     value zero is a null pointer constant. A named constant or
>     compound literal constant with a pointer type and a value null is
>     a null pointer but not a null pointer constant; it may only be
>     used to initialize a pointer object if its type implicitly
>     converts to the target type.
>
> That first sentence is so important, you’d think it would be in the main 
> text somewhere.

The definition of "null pointer constant" is in N3220 6.3.2.3,
(Conversions, Other operands, Pointers):

    An integer constant expression with the value 0, such an expression
    cast to type void *, or the predefined constant nullptr is called a
    *null pointer constant*.

6.6 makes it clear that named constants and compound literal constants
of integer type are integer constant expressions.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */